Real-Time Raman Monitoring and Control of the Catalytic Acetalization of Glycerol with Acetone over Modified Mesoporous Cellular Foams

Abstract

The acetalization of glycerol with acetone over modified mesoporous cellular foam materials has been widely investigated using in situ Raman spectroscopy during reaction. Mesoporous cellular foams (MCFs) modified by niobium or tantalum and (3-mercaptopropyl)trimethoxysilane (MP) followed by H2O2 treatment were used as catalysts in the acetalization of glycerol with acetone. The influence of the type of catalyst, which determines the solid texture and number of Brønsted acid sites, and different reaction parameters, such as reaction time, reaction temperature, glycerol/acetone ratio, and catalyst amount on acetalization reaction, were investigated. The results obtained in the characterization of the catalysts show that the materials obtained differ in the number of Brønsted acidic sites. Raman spectroscopy provides noninvasive insight during acetalization of glycerol with acetone in the presence of acid heterogeneous catalysts. The progress of the acetalization reaction was monitored following the variation in intensity of characteristic Raman bands and using chemometric analyses. The results obtained by real-time Raman monitoring confirm the mechanism proposed for the reaction, which proceeds via the formation of the 3-(2-hydroxypropan-2-yloxy)propane-1,2-diol intermediate, whose presence is confirmed by Raman spectroscopy. Under optimal reaction conditions, the 5-membered ring ketal 2,2-dimethyl-1,3-dioxolane-4-yl methanol (solketal) was obtained with the highest selectivity (99%). Raman monitoring enables real-time control of the reaction, thus enabling the optimization of reaction conditions for a more efficient reaction. Raman monitoring illustrates the reversibility of the reaction upon evaporation of acetone, even under reflux.